pptp is easier to setup and use, here is information useful to change the port:
the client config is to tweak a registry value: TcpPortNumber, for detail google search the content with the value.

and this the info used to tweak the pptpd port on the linux server with iptable:

http://blog.softlayer.com/2011/iptables-tips-and-tricks-port-redirection/

Also here is a guide on the command line tool in windows to trouble shoot the network issues:
Command-line utilities:

http://technet.microsoft.com/en-us/library/cc757819%28WS.10%29.aspx